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AttoPilot review, Part 1: The PCB board

Posted by Chris Anderson on April 2, 2009 at 11:39pm

I just got an AttoPilot in and plan to review it in several parts. Today's part: the PCB board. As you might expect from a former Intel engineer, Dean Goedde has done a great job of PCB design. Neat trace layouts, good noise protection and robust components. The board is based on a 5Mhx Parallax Propeller chip, with 8 cores. It has a differential pressure sensor for speed and a single pressure sensor for altitude. It also has 512k of on-board memory in addition to that in the Propeller chip. Click on the photo and you'll be taken to Flickr, where you can mouse over the components to find out what they are AttoPilot board top And here's the bottom of the board. Click on this one, too, to find out what the components are: AttoPilot board bottom
Tags: attopilot
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  • Dean June 16, 2009 at 6:53pm
    Let me explain further my rationale here:
    1) Most sUAS that I have tested don't need to go much above 110 km/h, so 200 km/h is more than a little buffer
    2) My autopilots auto-scale the PI and D gains in the 50Hz attitude control loop based on airspeed, so I can't just stop estimating body-forward airspeed at some limit like 200 km/h. Thus, I need a method to extend the airspeed estimation above the diff P sensor
    3) Unless you are flying in a hurricane or near a tornado, the wind speed will be << 200 km/h. Therefore, if the sUAS is flying with an airspeed > 200 km/h, we can more or less ignore that there is wind; i.e. ground track speed corrected for pitch of the aircraft is ~ airspeed.

    That's my rationale. It distinctly draw a practical line in the sand and doesn't get too caught up in worrying about 2nd and 3rd order effects. Sure, armchair engineers can be technically correct and state "but there is actually wind, and it affects the airspeed even if the sUAS is moving fast, so using GPS speed is not perfect". Thinking too hard about the details isn't the problem, the problem is not being able to differentiate the dominate effects from the trivial, and getting paralyzed on details that don't matter above the noise floor.
  • Dean June 16, 2009 at 6:27pm
    "On the subject of Airspeed and the 200km/h limit - It should be noted that GPS - aka groundspeed - and airspeed are not the same thing"

    Uhhh, yeah - that's why I described taking ground speed and converting to body-forward speed by dividing the ground speed by Cos(pitch). It works out. What is the percieved problem?

    200 km/h is about 125 mph. Pretty fast and above most sUAS unless you are talking about a funjet at full throttle.
  • Jack Crossfire June 16, 2009 at 11:50am
    > I will be pretty pissy and sensitive until the day I break even.

    Another Dave Perry is born. Now some reading material 4 U entrepreneurs while U wait to finish your day jobs & get back to work:

    Tips for Startup Companies



    best way to escape 9-5 wage slavery


    Best quote: "Without using other folks' money, it is hard to do much of anything."
    Tips for Startup Companies
  • Dean June 16, 2009 at 10:41am
    I was being immature stating it that way and trying to get a jab in. Yes, I was pretty upset at the time that Atto pics and an attempted dissection were all over DIY Drones.... The hardware is but a tiny piece of why and how my autopilot works (95% of it is hard-won code based on endless testing), but there are many many hard-won little victories even in component and layout choices and why should I just hand them over to other people? I say "let them spend $45k on components and equipment in 2008 and quit their lucrative day job in order to really focus on this.. and go into debt like I did." I will be pretty pissy and sensitive until the day I break even.

    Regarding the MPXV7002-DP sensor for airspeed... if I chose the 1-sided sensor like Jordi suggested, then how would people be able to instal BOTH the static and dynamic ports? The 1-sided sensor has a vent hole I believe on the bottom of the package... how is that usable? Besides, pressure vs Airspeed curve with my +/- 2k range gets up to at least 200 km/h... who out there with sUAS is going to fly above 200km/h? and anyway, I already thought of that and my code switches to GPS speed (with cosine(pitch) correction) above 200km/hr, so I am not limited in Atto.
  • T3
    Krzysztof Bosak June 16, 2009 at 2:41am
    "Jordi - I use the 2-sided MPXV7002 because in AttoPilot code, I use the absolute value of the differential pressure, so that if for some weird reason a person voided their warranty by taking the Atto out of the case and broke off one of the 2 pressure ports, they coulde just plug the Pitot tube into the other port. "
    Dean, decide yourself, are you HAPPY to see your customers doing reverse engineering or not.
  • T3
    Krzysztof Bosak June 16, 2009 at 2:38am
    The reveng is making possible to calculate Dean's profitability margin and to deal with him harder when going large series. This is undertandable he is angry because 80-90% of the price of every single electronics you use are software engineers. The PCB and components are nothing as they are, yet the negotiator ordering 100pcs will exploit this thread to the max, exactly going into Dean's income for the past 2 years of his work.
    All fluids and rare metals you need to make a human are under 1USD. Yet, you cannot buy it even for 1e6USD.
  • VoiceOfReason April 5, 2009 at 6:33pm
    I'm pretty sure I get the site concept, and how Dean designed his board is indeed relevant and instructive to a group trying to make their own autopilots. But that isn't why he sells his product. That is why it falls into the reverse engineering category, and why I think (not speaking for him) that he is entitled to be bothered by the dissection.

    That's o.k.! You are well within your rights (I believe) to do this. But there is also no harm in acknowledging that it was a baby step at a reverse engineering process so that others could possibly use this route in their own DIY quests. And that when Dean sells someone an autopilot, that isn't the intended use.

    I'm not trying to start a fire here. You're right, I should get one and test it myself and contribute. This site isn't about product reviews to help inform consumers, it is a hobbyist site, and I have benefited from the information on it so I should probably give back. For right now though, I'm going to slink back to the back row of the class now if I may :)
  • 3D Robotics
    Chris Anderson April 5, 2009 at 6:01pm
    VoR, I think you're confused about the point of this site. It's "DIY" drones, for people who want to learn how to make their own autopilots. How Dean designed his board is relevant and instructive, not "nosy".

    As is clear from Part 1 and Part 2, this review is coming out in several parts. We'll get to performance and flight comparisons later. I fully expect AttoPilot to vastly outperform ArduPilot (as one would expect from the 5x difference in price). If you've been paying attention here, you'll know that we are the huge AttoPilot supporter.

    At any rate, I invite you to review AttoPilot yourself here. You can do it your own way, and take as little or as much room as you want. If, after our review series is finished, you think we've missed something, please feel free to add it yourself. We're just the hosts here, but the community makes the site.
  • VoiceOfReason April 5, 2009 at 5:45pm
    I wouldn't apologize if I were you Dean. Remember, the DIY guys are biased...they have their own "baby" that they are promoting. A product review looks at product features and compares marketing claims to real performance. If you do 50Hz updates and everyone else does 10 Hz updates, then that is a feature worthy of review. How you physically do it only matters to people looking to reverse engineer your hard work for their benefit.

    A flight test comparison looking at performance on the same airframe between Attopilot and Ardupilot or other unit would be a real review that would be worthy of discussion.

    This was just people being nosy about what is under the hood, and I think its natural to be a little miffed.
  • Dean April 4, 2009 at 9:57pm
    And - my apologies... I am EXTREMELY sensitive about my baby. I am almost out of my first stock of units (4 left, yeah!) but need to sell many more to get out of debt. I have almost ruined myelf financially to get this to market. I resisted releasing it sooner because documentation was not up to snuff, and that part of it is still rough, but then here comes the tax man, so I started sales with the knowledge that for these first units I'll be forced to give more direct 1:1 support to customers.

    BTW - I have no plans to make paper manuals... it is all .pdf and people can print out selected pages if they feel the need. Save a tree!
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